An internal combustion engine is designed to burn fuel to generate heat energy and to obtain power by converting the generated heat energy into kinetic energy. Not all of the heat energy can be converted to kinetic energy, because a portion of the heat energy is discharged into the atmosphere in the form of exhaust gas. The loss of heat energy through the exhaust gas reduces the efficiency of the internal combustion engine. A technique is known in which an exhaust heat recovery device is attached to the exhaust pipe, and a portion of the heat energy is recovered from the exhaust gas by the exhaust heat recovery device.
Japanese Patent Application Laid-Open Publication No. 2009-30569, for example, discloses an exhaust heat recovery device. The structure of this exhaust heat recovery device is described with reference to FIG. 13 hereof.
As shown in FIG. 13, the exhaust heat recovery device 100 is composed of a bypass flow channel 101 for circulating exhaust gas, the bypass flow channel being connected to an exhaust pipe extending from an internal combustion engine; a branching channel 103 branched at a right angle to the axis of the bypass flow channel 101 from the vicinity of an inlet 102 of the bypass flow channel 101; a valve 105 capable of opening and closing, for blocking an outlet 104 of the bypass flow channel 101; a valve shaft 106 for rotating the valve 105; a curved pipe 107 which extends from the valve 105; a case 108 for housing the bypass flow channel 101, the valve 105, and the curved pipe 107 at once; an exhaust heat recovery flow channel 111 for circulating the exhaust gas fed from the branching channel 103, the exhaust heat recovery flow channel being formed in the case 108; and a heat exchanger 112 which fits in the exhaust heat recovery flow channel 111. The bypass flow channel 101 is a flow channel for bypassing the heat exchanger 112.
The medium of the high-temperature side of the heat exchanger 112 is the exhaust gas, and the medium of the low-temperature side is a coolant of the internal combustion engine.
The valve shaft 106 for supporting the valve 105 is urged toward the valve-closing side by a torsion spring. When the flow rate of exhaust gas through the bypass flow channel 101 is high, the gas pressure overcomes the urging force of the torsion spring. As a result, the valve is opened. When the flow rate of exhaust gas is low, the valve is closed by the action of the torsion spring.
The valve shaft 106 is also rotated by a thermo-actuator via the torsion spring. The coolant for cooling the internal combustion engine is passed through the thermo-actuator. When the coolant is at a high temperature, the valve shaft 106 is rotated toward the valve-open side by the thermo-actuator, and when the coolant is at a low temperature, the valve shaft 106 is rotated toward the valve-closed side.
The coolant is at a low temperature when the internal combustion engine is started. The flow rate of exhaust gas is low during idling. The valve is closed under these conditions. Exhaust gas flows to the exhaust heat recovery flow channel 111 without flowing to the bypass flow channel 101. Heat is recovered by the heat exchanger 112, and the coolant is heated.
When the flow rate of exhaust gas is high even at startup of the internal combustion engine, the valve opens and the exhaust gas flows to the bypass flow channel 101. The bypass flow channel 101 has minimal flow channel resistance, and is therefore capable of circulating a large amount of exhaust gas.
The coolant reaches a high temperature once operation has continued for a certain amount of time. The valve is opened by the action of the thermo-actuator, and the exhaust gas flows to the bypass flow channel 101. The reason for this is that there is no need for the coolant to be warmed by the heat exchanger 112 when the coolant is at a high temperature.
The case 108 is formed by welding together two case halves that are divided in the front-back direction of the drawing. Before welding, the bypass flow channel 101, the valve 105, the valve shaft 106, and the heat exchanger 112 are placed in a case half. A first seal 113 is wrapped around the branching channel 103, and a second seal 114 is wrapped around the bypass flow channel 101. The other case half is then placed over the first case half, and the case halves are welded together.
Leakage and backflow of exhaust gas are prevented by the first seal 113 and/or the second seal 114.
The first seal 113 and/or the second seal 114 cannot be replaced after the case halves are welded together. However, the first seal 113 and/or the second seal 114 become worn over the course of operation. As wear progresses, the sealing ability of the seals decreases, and backflow of exhaust gas occurs. Assembly is also made inconvenient by the labor of packing the bypass flow channel 101, heat exchanger 112, and other components in the case halves and then welding the case halves. As a result, the cost of the exhaust heat recovery device increases, and the use of exhaust heat recovery devices is less easily adopted.
In order to promote the use of exhaust heat recovery devices, there is a need for an exhaust heat recovery device that is easily assembled.
When the exhaust heat recovery device 100 is mounted in a vehicle having significant space limitations, a curved pipe 115 is frequently connected to the inlet of the bypass flow channel 101. The use of a curved pipe 115 enables the duct length to be maintained in a limited space. When a curved pipe 115 is used, a portion of the exhaust gas impinges on the inside surface of the bypass flow channel 101, as indicated by the arrow (1) in FIG. 13. This impingement causes the flow to become disordered, and there is a risk of inability to maintain the flow rate of the exhaust gas.
There is therefore a need for an exhaust heat recovery device in which a smooth flow of exhaust gas is maintained even when a curved pipe is connected to the inlet.